Method swap

src/bsh/CallStack.java:108–113

Swap in the value as the new top of the stack and return the old value.

( NameSpace newTop )

		value.
	*/
	public NameSpace swap( NameSpace newTop ) {
		int last = stack.size() - 1;
		NameSpace oldTop = stack.get(last);
		stack.set( last, newTop );
		return oldTop;
	}

	public int depth() {
		return stack.size();